• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2008.03a
• /
• pp.442-447
• /
• 2008

A numerical analysis has been conducted to investigate and characterize the unsteadiness of flow structure and oscillatory vacuum pressure inside of a supersonic diffuser equipped to simulate the high-altitude rocket test on the ground. A physical model of concern includes a rocket motor, a vacuum chamber, and a diffuser, which have axisymmetric configurations, using nitrogen gas as a driving fluid. Emphasis is placed on investigating physical phenomena of very complex and oscillatory flow evolutions in the diffuser operating at very close to the starting condition, i.e. minimum starting condition, which is one of major important parameters in diffuser design points of view.

• 제어로봇시스템학회:학술대회논문집
• /
• 2005.06a
• /
• pp.2203-2206
• /
• 2005

A load flow and short circuit fault simulation of AC electrified railway distribution systems is presented with DIgSILENT PowerFactory software. Load flow of electrified railways distribution system with concerning multi train lines and dynamic characteristics of train load is studied for different time laps. The dynamic characteristics of train load in starting and braking conditions with different starting and stopping times and its moving positions makes the load flow complicated so there is a great need in studying the effects of electrified railways on load flow. Short circuit fault transients is also studied and simulated for both power system or traction distribution system and their effects on the operation of the train sets is investigated.

• 한국전산유체공학회:학술대회논문집
• /
• 2000.05a
• /
• pp.39-44
• /
• 2000

Two-dimensional Navier-Stokes codes are used to simulate the shock tunnel in Konkuk university. In order to design experiments in impulse facilities properly and to interpret data from such facilities, it is necessary to understand how the flow approaches steady state. This is done by determining the transient flow field and flow establishment time around a given model. This will be accomplished by developing appropriate CFD codes which solve the Navier-Stokes equations, and simulating the starting process and resulting unsteady viscous flow phenomena. The starting process in a shock tunnel consists of multiple shock interactions and contact discontinuities, which are difficult to solve with the classical shock capturing schemes. A recently developed high resolution scheme is adapted for resolving the unsteady phenomena of those multiple shock interactions and contact surfaces during the starting process. The bifurcation phenomenon due to the interactions of the reflected shock from the end of the shock tube with the boundary layer generated by the incident shock becomes of particular interest. By comparing with the experiment results, the accuracy of the numerical analysis is validated and it is demonstrated that the properties which can hardly be obtained through the experiment can be estimated.

• Proceedings of the KIEE Conference
• /
• 2006.07b
• /
• pp.813-814
• /
• 2006

The squirrel case induction motor has widely used in the driving of the blowers but it is low efficiency and hard to control. So, the damper is used for the control of a flow and it cause to low the driving efficiency. Our laboratory has proposed the single-phase SRM(switched reluctance motor) for driving blowers. It has salient pole structure and can be reduced a number of semiconductors than three-phase SRM. But it can not be starting by itself and has heavier torque ripple than three-phase SRM. For self-starting the single-phase SRM is required the starting device which place the rotor at the rising inductance slope. On this paper, the electromagnet starting device is designed to generate the starting torque and to fix the rotating direction of the single-phase SRM which is fabricaed to use a blower.

• Transactions of Materials Processing
• /
• v.20 no.8
• /
• pp.611-618
• /
• 2011

Flow forming is an incremental forming process in which rollers are used to form cylindrical parts with repeated turning of both roller and starting material. Both sheet and tube can be used as the starting material. The process is highly useful for producing hollow shaped parts from a tube, with the benefit of the average strain in the final shape being significantly lower than that from a sheet material. In the present study, the flow forming process was studied and optimized for producing a hollow shaped part from seamless steel tube by both experiment and numerical analysis. Upon considering the difficulty of forming seamless steel sheet, the thickness reduction was distributed over several tool paths. In the end, an optimum process condition was attained, and the experiment verified the simulation results.

• International Journal of Aeronautical and Space Sciences
• /
• v.9 no.2
• /
• pp.98-106
• /
• 2008

The motive gas of a supersonic ejector is supplied from different sources depending on the application. The performance of an ejector that is represented by the secondary flow pressure, starting and unstarting pressures heavily depends on the molecular properties of the motive gas. The effects of specific heat ratio of the motive gas were investigated experimentally for an axi-symmetric annular injection type supersonic ejector. Both the starting pressure and unstarting pressure, however, decreased with the increase of the specific heat ratio of the motive gas. It was discovered that the secondary flow pressure increased as the specific heat ratio of the motive gas decreased even if the stagnation pressure of the motive flow was invariant. However, when the motive gas flow nozzle area ratio is large enough for the motive gas to be condensed, different tendency was observed.

• Proceedings of the KSME Conference
• /
• 2005.11a
• /
• pp.75.2-75.2
• /
• 2005

• 전기의세계
• /
• v.22 no.2
• /
• pp.23-27
• /
• 1973

An initial starting voltage, ignition time, glow current and blink of the flow starter are changed rapidly in initial using. therefore an ageing is required to stabilize the initial characteristics. According to the experiments, it is proved that the ageing time for the starting voltage and glow current takes 3 minutes and 5 minutes for ignition time and blink.

• Journal of Korea Water Resources Association
• /
• v.35 no.3
• /
• pp.251-259
• /
• 2002

Flow characteristics occurring a side-weir overflow in rectangular channel is investigated in this study. A numerical model based on the two -dimensional shallow-water equations is employed to review the factors influencing on the side- weir overflow discharge and the change of flow depths and velocities. It is found that the discharge coefficient which has the most significant influence on the overflow is affected by geometric characteristics of a side-weir, Froude number of the main channel flow and the flow depth of the main channel at the starting point of a side-weir. And the discharge coefficient applicable to a practical design of a side-weir is proposed by deriving a relationship between Froude number of the main channel flow at the starting point of a side-weir and Froude number of the main channel flow.

• 전기의세계
• /
• v.19 no.5
• /
• pp.1-7
• /
• 1970

Starting from the review of signal flow graphs and flow graphs, this paper gives an example of sampled-data systems for Sedlar & Bekey's formulation. In this purpose it discussed the difference between Mason's signal-flow graphs and Coates flow graphs for drawing th flow graph of a linear system, and then a new flow-graph symbol introduced in order to distinguish between continuous and discrete systems. Thus, the paper is analysed and compared with a sampled-data systems between conventional methods and new method of signal flow graphs.